Nanostructures have been found to impart useful properties on surfaces of articles. These useful properties include useful optical properties, such as, for example, reflection reduction of plastic substrates, useful mechanical properties, such as, for example, surface modification for improved adhesion, and for creating features on surfaces that can be useful in, for example, drug delivery.
Many methods exist to generate nanostructure on surfaces of articles. For example, plasma etching is a useful method that has been used to generate nanostructures. A type of plasma etching, reactive ion etching (RIE), has been widely employed in the semiconductor industry to produce submicron features useful in electronics. However, when the feature sizes reach below about 200 micrometers, charging effects of the surface features prevent pattern transfer of features having high aspect ratios. Recently, high density plasma processes have been developed that can produce nanostructures in the sub-100 micrometer range. The semiconductor industry is currently working on the fabrication of features with around 40 nm resolution using patterning and pattern transfer based on advanced plasma processing tools.
Known methods for creating the subwavelength surface structure tend to be complicated and expensive batch processes, however. For example, the method disclosed in U.S. Pat. Publ. No. 2005/0233083 (Schultz et al.) involves bombarding a polymeric surface with Ar/O2 plasma under vacuum conditions of less than 0.5 mTorr. This requirement of extreme vacuum conditions limits the commercial viability of the method. U.S. Pat. No. 4,374,158 (Taniguchi et al.) describes a gas activation method for creating subwavelength surface structure. This batch process employs a plasma asher to isotropically etch samples in an oxygen-containing gas ambient. The resulting isotropically etched surfaces require an additional coating to provide durability.
Plasma treatment has also been used to produce antireflective surfaces on polymeric substrates, including transparent polymeric substrates. These treatments are all batch processes and can produce only limited antireflective regions on the substrates. There is a need for new methods of producing nanostructures on substrates. There is a need for new methods that are faster, more economical, and capable of producing nanostructures on large areas for uses, for example, on large displays. There is a need for methods to produce nanostructures on surfaces in a substantially continuous manner.